IntroductionTo examine the influence of adjuvant chemoradiation therapy (CRT) on survival, stratified by varying numbers and level involved of metastatic lymph nodes in patients with head and neck squamous cell carcinoma (HNSCC). MethodsPatients who underwent surgery for metastatic, negative margin HNSCC without extranodal extension were retrospectively enrolled and divided into two groups based on adjuvant therapy received: radiotherapy (RT) and CRT. The impact of RT versus CRT, stratified by the number of positive lymph nodes and the level involved, on Disease-Free Survival (DFS) and Overall Survival (OS) was analyzed. ResultsFollowing propensity score matching, a total of 580 patients were included. The burden and level of lymph node metastasis were independent predictors of poorer survival. Among patients with no more than two positive lymph nodes or involvement of levels I-III, the addition of chemotherapy to RT did not demonstrate a significant improvement in prognosis. However, in patients with three or more positive lymph nodes, CRT showed improved DFS and OS compared to RT. In patients with involvement of levels IV-V, the addition of chemotherapy to RT resulted in a significant 24% reduction in the risk of recurrence and a 20% decrease in the risk of death. ConclusionIncorporation of adjuvant chemoradiation can lead to a favorable prognosis in patients with metastatic HNSCC. This impact was notable in cases where there were three or more positive lymph nodes or involvement of levels IV-V.